1. Field of the Invention
The present invention relates to a sensitivity-calibration circuit for an HC analyzer for detecting the concentration of "HC gases" such as methane (CH.sub.4) and ethane (C.sub.2 H.sub.6) as an n-hexane reduced gas-concentration value.
2. Description of the Prior Art
Although the sensitivity-calibration in a HC analyzer of this type should be always carried out using the standard n-hexane gas (having a known concentration) in a nature of things, in fact it is carried out using substitute gases since n-hexane gas has an unstable property of very easily being liquefied.
That is to say, the sensitivity-calibration has been carried out in the following manner:
At first, in the initial adjustment of a HC analyzer, at first an appointed sensitivity-calibration has been carried out by the use of a standard n-hexane gas having a known concentration and then a standard propane gas also having a known concentration C.sub.p has been passed through the HC analyzer to measure the concentration thereof. A scale factor P.sub.c inherent to said HC analyzer is determined from the measured value (corresponding to the n-hexane reduced gas-concentration C.sub.N of the standard propane gas-concentration C.sub.p) by the HC analyzer. The scale factor P.sub.c (for example, the scale factor for an n-hexane gas-concentration: 0.521) is then recorded on a display label and is affixed to the HC analyzer.
Now, said scale factor P.sub.c is determined by the calculation based on the following equation [I]: EQU P.sub.c =C.sub.N /C.sub.p [I]
wherein
C.sub.N : a measured value by the HC analyzer (a n-hexane reduced gas-concentration value of a standard propane gas) PA0 C.sub.p : a standard propane gas-concentration.
And, in the usual calibration when the analyzer requires recalibration after the initial adjustment, at first the n-hexane reduced gas concentration value C.sub.N of standard propane gas is determined in accordance with the following equation ([II] which is a modification of said equation [I]) on the basis of the known concentration C.sub.P of standard propane gas to be used (this is recorded on a display label affixed to a gas cylinder in a manner of, for example, concentration: 1,862 ppm [C.sub.3 H.sub.8 ]) and the scale factor P.sub.c inherent to the HC analyzer and previously recorded on the display label is also affixed to the HC analyzer in the above described manner. EQU N-hexane reduced gas-concentration value C.sub.N EQU =the concentration C.sub.p of standard propane EQU gas.times.the scale factor P.sub.c (=1,862.times.0.521=about 970) [II]
Then, the standard propane gas is passed through the HC analyzer and the sensitivity-calibration circuit in the HC analyzer is adjusted so that an output of the HC analyzer may indicate the n-hexane reduced gas-concentration value C.sub.N (for example 970 ppm) determined in the above described manner.
However, with the above described conventional means, as is obvious from the technique described above, each HC analyzer has a scale factor P.sub.c which is inherent and different due to minor differences in their optical systems. Moreover, since the scale factor P.sub.c is usually a complex value, such as 0.521, consisting of many digits, a disadvantage has occurred in that complicated calculations of multiple digit numbers on the basis of the above described equations must be carried out for every calibration after the initial adjustment.